Classifications

• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K7/00—Constructional details common to different types of electric apparatus
  • H05K7/20—Modifications to facilitate cooling, ventilating, or heating
  • H05K7/20709—Modifications to facilitate cooling, ventilating, or heating for server racks or cabinets; for data centers, e.g. 19-inch computer racks
  • H05K7/20718—Forced ventilation of a gaseous coolant
  • H05K7/20745—Forced ventilation of a gaseous coolant within rooms for removing heat from cabinets, e.g. by air conditioning device
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F24—HEATING; RANGES; VENTILATING
  • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
  • F24F11/00—Control or safety arrangements
  • F24F11/30—Control or safety arrangements for purposes related to the operation of the system, e.g. for safety or monitoring
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F24—HEATING; RANGES; VENTILATING
  • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
  • F24F11/00—Control or safety arrangements
  • F24F11/70—Control systems characterised by their outputs; Constructional details thereof
  • F24F11/72—Control systems characterised by their outputs; Constructional details thereof for controlling the supply of treated air, e.g. its pressure
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F24—HEATING; RANGES; VENTILATING
  • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
  • F24F11/00—Control or safety arrangements
  • F24F11/70—Control systems characterised by their outputs; Constructional details thereof
  • F24F11/80—Control systems characterised by their outputs; Constructional details thereof for controlling the temperature of the supplied air
  • F24F11/81—Control systems characterised by their outputs; Constructional details thereof for controlling the temperature of the supplied air by controlling the air supply to heat-exchangers or bypass channels
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F24—HEATING; RANGES; VENTILATING
  • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
  • F24F2110/00—Control inputs relating to air properties
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K7/00—Constructional details common to different types of electric apparatus
  • H05K7/20—Modifications to facilitate cooling, ventilating, or heating
  • H05K7/20709—Modifications to facilitate cooling, ventilating, or heating for server racks or cabinets; for data centers, e.g. 19-inch computer racks
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F24—HEATING; RANGES; VENTILATING
  • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
  • F24F11/00—Control or safety arrangements
  • F24F11/70—Control systems characterised by their outputs; Constructional details thereof
  • F24F11/72—Control systems characterised by their outputs; Constructional details thereof for controlling the supply of treated air, e.g. its pressure
  • F24F11/74—Control systems characterised by their outputs; Constructional details thereof for controlling the supply of treated air, e.g. its pressure for controlling air flow rate or air velocity
  • F24F11/75—Control systems characterised by their outputs; Constructional details thereof for controlling the supply of treated air, e.g. its pressure for controlling air flow rate or air velocity for maintaining constant air flow rate or air velocity
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K7/00—Constructional details common to different types of electric apparatus
  • H05K7/20—Modifications to facilitate cooling, ventilating, or heating
  • H05K7/20709—Modifications to facilitate cooling, ventilating, or heating for server racks or cabinets; for data centers, e.g. 19-inch computer racks
  • H05K7/20836—Thermal management, e.g. server temperature control

Definitions

• CRAC computer-room air conditioning
• Each CRAC unit comprises one or more fans to draw data centre air into the CRAC unit.
• the in-drawn air is cooled as it passes through the CRAC unit, for example by exposure to a heat exchanger comprising chilled water, and expelled into a cold area of the data centre to cool the computing equipment.
• Each item of computing equipment generally comprises a fan to draw air therethrough to cool electronic components and/or devices within the computing equipment. Air is expelled from the computing equipment into a hot area of the data centre for return to the one or more CRAC units.
• Figure 1 illustrates air pressure against airflow within a data centre having 1, 2 or 3 operational CRAC units and between one and twenty four items of computing equipment each having an internal fan.
• Airflow and pressure for a single CRAC unit is represented by line 101; line 102 represents airflow and pressure for two CRAC units operating in parallel; and line 103 represents three CRAC units operating in parallel.
• Airflow and pressure for one item of the computing equipment is represented by line 104, whilst pressure and airflow for twenty four items of computing equipment arranged in parallel is shown by line 105.
• Airflow through intermediate numbers of items of computing equipment is shown in Figure 1, although each line is not individually labelled for clarity. It will be noted that twenty four items of computing equipment are described for example only and the data centre may comprise further items of computing equipment.
• An operational variance 106 in controlling airflow through each CRAC units exists.
• the variance in controlling the airflow through three CRAC units is shown in Figure l(a) and the effect 107 of the CRAC unit operating variance on the twenty four items of computing equipment is shown in Figure l(b) which represents a close-up of the same part in Figure l(a).
• a relatively small variation in CRAC unit air pressure has a relatively large effect on the cooling system and cooling of the computing equipment. This is troublesome for the computing equipment, particularly since many complex items of computing equipments, such as servers and the like, include a plurality of temperature sensors and complex cooling control systems which are greatly affected by the variation in CRAC unit airflow output.
• Figure 1 shows an illustration of pressure against airflow for a number of different CRACs and items of computing equipment
• Figure 3 shows a schematic illustration of a data centre according to an embodiment of the invention
• FIG. 7 illustrates a data centre cooling system according to embodiments of the invention which incorporates redundancy between CRAC units
• Figure 8 illustrates a data centre cooling system according to a further embodiment of the invention which incorporate redundancy between CRAC units
• a bypass airflow 240 is present in the proximity of the computing equipment 202.
• the bypass airflow 240 is cooled air from output from the CRAC unit, mixed with any negative pressure airflow 220, which bypasses the computing equipment 202 and generally returns to the CRAC unit 201 without having provided cooling to the computing equipment 202.
• the remaining air 250 passes through the computing equipment 202 and is heated by the computing equipment 202 to an example temperature of 35 0 C.
• the expelled air from the computing equipment mixes with the bypass airflow 240 to form a resulting airflow 260 having an example temperature of 25 0 C which is returned to the CRAC 201 unit for cooling.
• a recirculation airflow 270 is formed.
• the recirculation airflow 270 is warmed air from the computing equipment 202 which recirculates to re-enter the computing equipment 202.
• the recirculation airflow 270 is at a temperature of 35 0 C.
• the resultant combined airflow 250 into the computing equipment 202 is at an example temperature of 24 0 C, depending on the ratio of recirculated airflow 270 to supply airflow 230
• segregation between cold and hot air areas is used to control airflow there-between. Segregation between cold and hot air areas is achieved through appropriate construction of air-tight barriers, such as walls, doors, computing cabinets etc.
• the recirculation airflow is prevented, or at least substantially minimised, by the segregation.
• a negative pressure airflow may exist in the data centre 200. However, known design techniques may be used to minimise the negative pressure airflow and therefore it will not be further discussed.
• a predetermined level of bypass airflow is maintained in the data centre.
• the bypass airflow is measured and the output airflow of the one or more CRAC units is controlled in response to the measured bypass airflow, such that the bypass airflow is maintained at the predetermined level.
• the predetermined level is a minimum level of bypass airflow, at or close to which the bypass airflow is maintained.
• the bypass airflow is maintained within a predetermined range.
• a small positive pressure is maintained at an air inlet to computing equipment, regardless of an operating load of the computing equipment.
• air supplied to the computing equipment is the same as that leaving one or more CRAC units supplying that air i.e. recirculation of air is minimised or eliminated, and only a necessary amount of air for cooling the computing equipment and maintaining the small level of bypass airflow is supplied.
• problems associated with CRAC unit fans and computing equipments fans in series are reduced.
• Embodiments of the present invention will be described with reference to cold and hot portions of the data centre. It is understood that the cold portion is segregated from the hot portion and contains comparatively cool air supplied from one or more air conditioning units, whilst the hot portion contains warm air expelled from the computing equipment.
• the data centre 300 comprises a CRAC unit 310, computing equipment 320, a flow meter 330 and a control unit 340.
• the CRAC unit 310 includes a cooling unit 311 which is arranged to cool air being moved through the CRAC unit by a fan 312.
• the cooling unit 311 may be a heat exchanger having a cooled liquid, such as water, passing through one channel thereof whilst the air passes through another channel, such that heat is absorbed by the liquid from the air to thereby output a cooled airflow 315 from the CRAC unit 310.
• the cooled air 315 emitted from the CRAC unit 310 is expelled into a cold portion 350 of the data centre 300.
• the cold portion 350 is segregated from a hot portion 360 of the data centre 300 by a barrier 370.
• Air is drawn through the computing equipment 320 from the cold portion 350 by one or more fans (not shown) within a housing of the computing equipment 320. Air heated by the computing equipment 320 is expelled from the computing equipment 320 into the hot portion 360 of the data centre 300.
• the flow meter 330 is located in an aperture of the barrier 370 segregating the cold and hot portions 350, 360 of the data centre 300.
• the flow meter 330 is located in a decoupling area of the data centre 300.
• the decoupling area is a common area in the data centre 300 between fans present within the computing equipment 320 and the CRAC unit 310. Ideally, the decoupling area is as large as practically possible to achieve effective decoupling of airflows. However, in practical embodiments, the decoupling area has a limited size to achieve sufficient decoupling.
• a bypass airflow 380 from the cold portion 350 to the hot portion 360 is allowed to flow through the flow meter 330, such that the flow meter 330 measures a velocity of the bypass airflow 380.
• a bypass airflow signal 331 indicative of the measured velocity is output by the flow meter 330 to the control unit 340.
• the flow meter 330 is a flow grid which forms the aperture through the segregation between the cold and hot portions. That is, the bypass airflow between the cold and hot portions flows through the flow grid.
• the flow grid is formed by a parallel set of tubes connected by manifolds. The tubes are perforated and provide a single differential pressure signal 331 which is proportional to the square of air flow velocity through the flow grid.
• the flow grid is a multi-point averaging device which determines a flow rate by measuring an average pressure drop across the flow grid.
• the flow grid may be a Wilson flow grid.
• a rotary flow meter may used to measure the bypass airflow rate.
• the bypass airflow signal 331 is provided to the control unit 340, which controls an airflow rate of the CRAC unit 310 in response to the bypass airflow signal 331.
• the control unit 340 is arranged to output a CRAC unit control signal 341 to control a speed of the fan 312 to maintain the bypass airflow 380 at a predetermined level. That is, the speed of the fan 312 is adjusted according to the velocity of the bypass airflow 380 through the flow meter 330.
• the speed of the fan 312 may be controlled such that the bypass airflow 380 is maintained to, for example, between 1 and 5% of the total CRAC unit 310 output airflow 315.
• the speed of the fan 312 is reduced, less energy will be consumed by the CRAC unit.
• control signal 341 is provided to a mechanical actuator arranged to control a cross-sectional area of the aperture in the segregation between the cold and hot portions, such that the bypass airflow rate may be controlled in response to the control signal 341 by increasing or decreasing the cross sectional area of the aperture.
• control unit 340 Whilst the control unit 340 has been described in conjunction with Figure 3 as a separate entity, in other embodiments the control unit 340 may form part of the CRAC unit 310. In these embodiments the CRAC unit 310, and the control unit 340 located therein, is arranged to receive the bypass airflow signal 331 and the output of the CRAC unit 310 is controlled in response thereto. Furthermore, whilst the control signal 341 is shown as controlling a single CRAC unit 310, a plurality of CRAC units may be controlled by the control signal 341.
• the inefficient recirculation airflow is prevented, or at least minimised, by the segregation 370 of the cold and hot portions 350, 360 of the data centre 300 and the airflow output from the CRAC unit 310 which passes through the computing equipment 320 is managed by determination of the bypass airflow 380 and control of the CRAC unit 310 output in response thereto by the control unit 340.
• FIG. 4 A further embodiment of the present invention will now be described with reference to Figure 4.
• the embodiment shown in Figure 4 may be referred to as a cold air containment data centre in which cold air is contained, whilst a majority of the data centre is filled with hot air.
• Figure 4(a) shows a vertical cross section through a data centre 400 which includes under- floor and over-head ducting or plenums, as will be described.
• Figure 4(b) shows a plan view of the data centre 400 taken from above computing cabinets present within the data centre 400.
• the data centre 400 includes a plurality of racks or cabinets 410, 420, 430, 440 housing computing equipment.
• the computing equipment is mounted in racks then blanking plates and/or brushes are used appropriately to segregate cold and hot portions of the data centre 400.
• computing equipment is mounted in four cabinets 410, 420, 430, 440, such that the data centre 400 is divided in an alternating manner into cold 451, 452 and hot 461, 462, 463 aisles. It will be realised that other numbers of cabinets 410, 420, 430, 440 may be included in the data centre 400.
• Cool air output by one or more CRAC units is supplied through an under-floor cold air plenum, or duct, 450 to first and second cold aisles 451 , 452.
• the cold aisles 451 , 452 are formed by segregation at each end of the computing cabinets 410, 420, 430, 440 including walls and/or doors. A majority of the air entering the cold aisles 451, 452 is drawn through the computing equipment cabinets 410, 420, 430, 440 to cool the computing equipment mounted therein.
• Fans present within the computing equipment in the cabinets 410, 420, 430, 440 draw air from the cold aisles 451, 452 through inlets in a front of each cabinet 410, 420, 430, 440 and through the computing equipment housing to cool internal components and devices. Air is expelled from the cabinets 410, 420, 430, 440 through outlets in a rear of each cabinet into the hot aisles 461, 462, 463 which form part of a hot portion 460 of the data centre 400.
• the hot portion 460 of the data centre 400 is present above and around the cabinets 410, 420, 430, 440 as shown in Figures 4(a) and (b).
• a flow grid 480, 490 is arranged in an aperture present in the segregation between each cold aisle 451, 452 and the hot portion 460 of the data centre 400 to allow a bypass airflow there-through.
• the bypass airflow is cold air which enters the hot portion 460 from the cold portion 450 without having cooled computing equipment.
• Figure 4(a) shows two different arrangements of flow grid.
• the flow grid 480 is arranged generally horizontally in a ceiling of the cold aisle 451 segregation, whereas in a right-hand cold aisle 452 the flow meter 490 is arranged generally vertically in a segregating wall extending upward from the cabinet 490.
• Air is returned to the CRAC unit(s) from the air portion 460 for cooling along a return air plenum 470 located over the hot portion 460. Air enters the return air plenum 470 through a plurality of apertures.
• a single air supply from one or more CRAC units is provided to the plurality of cold aisles 451, 452 and each of the flow grids 480, 490 outputs a bypass airflow signal.
• a control unit as described above although not shown in Figure 4, is arranged to receive the plurality of bypass airflow signals output by the flow grids 480, 490 and to detect when one or more of the measured bypass airflows drops below the predetermined bypass flow level. In response, the control unit is arranged to control the one or more CRAC units to increase an airflow rate of cooled air to the plurality of cold aisles 451, 452.
• each cold aisle 451, 452 may be supplied with cooled air by a dedicated CRAC unit by division of the cold portion 450, such that each cold aisle receives cooled air from the respective CRAC unit.
• the flow grid for each cold aisle 451, 452 is arranged to output the bypass airflow signal to the control unit to control airflow into the cold aisle according to the bypass airflow there-from. Either of these arrangements may be applied to the embodiments of data centres described herein.
• Figure 5(a) shows a cross section view through a data centre 500 and Figure 5(b) shows a plan view, as in Figure 4.
• the data centre 500 shown in Figure 5 may be referred to as a hot air containment data centre in which hot air expelled from computing equipment is contained, whilst a majority of the data centre contains cold air.
• computing equipment is arranged in four computing cabinets 510, 520, 530, 540 and cooled air from one or more CRAC units (not shown) is supplied via a cold plenum 550 to enter cold aisles 551, 552 between pairs of computing cabinets 510, 520 and 530, 540.
• Air is drawn in a front of each computing cabinet 510, 520, 530, 540 by fans present within computing equipment housed within the computing cabinets 510, 520, 530, 540 and is expelled through a rear of each cabinet into a plurality of hot aisles 561, 562, 563.
• the hot aisles 561, 562, 563 in Figure 5 are contained by vertically extending segregation between and upward of pairs of cabinets 510, 520 and 530, 540.
• An end of each hot aisle 561, 562, 563 between pairs of computing cabinets 510, 520, 530, 540 is enclosed by a wall, door or combination thereof.
• Figure 5(b) shows an end of one hot aisle 562 having a door 553 which allows access to the hot aisle 562.
• the hot aisle segregation extends upward to direct hot air toward apertures in a hot plenum 560 to return air to the one or more CRAC units.
• Each hot aisle 561, 562, 563 comprises a flow grid 570, 580, 590 arranged in an aperture of the segregation between the cold and hot portions 450, 460 of the data centre 500.
• the flow grid 570, 580, 590 may be arranged in a wall forming the segregation, to form a door, or a part thereof, of the hot aisle, or any other suitable location such that the bypass airflow between the cold portion 450 and the hot portion 460 may be measured and a bypass airflow signal output in response thereto to control one or more CRAC units as described above.
• Figure 6 shows a further embodiment of data centre 600 according to an embodiment of the present invention.
• Figure 6(a) shows a cross section view through a data centre 600 and Figure 6(b) shows a plan view, as in Figures 4 and 5.
• the data centre 600 shown in Figure 6 may be referred to as a cabinet exhaust containment data centre, since an exhaust of each computing cabinet is contained and directed to return hot air to a ceiling return plenum or duct.
• the data centre comprises four computing cabinets 610, 620, 630, 640 in which computing equipment is housed.
• a cold plenum 650 supplies cooled air from one or more CRAC units (not shown) which is fed into cold aisles 651, 652, 653, 654, 655 between the computing cabinets 610, 620, 630, 640.
• Air is drawn into the cabinets 610, 620, 630, 640 from the cold aisle through inlets by fans operating in the computing equipment. Hot air is then exhausted directly into a hot air return plenum 660 via upwardly extending exhaust containment.
• Each cold aisle 651, 652, 653, 654, 655 comprises a flow grid 670, 680, 690, 695 arranged in an aperture of the segregation between that cold aisle and the hot plenum 660 to allow a bypass airflow there-between which is measured by the respective flow grid 670, 680, 690, 695.
• the flow grids 670, 680, 690, 695 are arranged to allow the bypass airflow to directly enter the hot plenum 660 from the cold aisles 651, 652, 653, 654, 655.
• bypass airflow in an area is measured by a plurality of flow grids which are each arranged to output a respective bypass airflow signal.
• a plurality of bypass airflow signals are received by a control unit which is arranged to control one or more CRAC units.
• the flow grids outputting bypass airflow signals to control other CRAC units measure a reduced level of bypass airflow.
• the other CRAC units increase airflow to compensate for the CRAC unit having the reduced operation.
• a data centre 700 comprises a plurality of aisles between rows or computing cabinets.
• the data centre 700 has a hot air containment arrangement, similar to that previously described with reference to Figure 5.
• the data centre 700 comprises six rows of cabinets 711, 712, 713, 714, 715, 716 housing computer equipment, although it will be realised that the number of cabinets is merely for illustrative purposes. Interposing the rows of cabinets 711, 712, 713, 714, 715, 716 are alternating hot 761, 762, 763 and cold 751, 752, 753, 754 aisles.
• a first hot aisle 761 is located between the first and second rows of cabinets 711, 712; a second hot aisle 762 is located between the third and fourth rows of cabinets 713, 714; and a third hot aisle 763 is located between the fifth and sixth rows of cabinets 715, 716.
• the hot aisles 761, 762, 763 form a hot area of the data centre 700.
• a cold area 750 surrounds the cabinets 711, 712, 713, 714, 715, 716 and hot aisles 761, 762, 763.
• the cold area 750 includes the four cold aisles 751, 752, 753, 754 and further comprises under-floor ducting (not shown) through which cooled air is supplied to the cold aisles 751, 752, 753, 754 which interpose each pair of cabinets surrounding the hot aisles 761, 762, 763.
• Three CRAC units 721, 722, 723 are each arranged to receive hot air from the hot area of the data centre 700. It will be noted that the location of the CRAC units 721, 722, 723 in Figure 7(a) is merely for illustrative purposes and the CRAC units may be located internal or external to the data centre 700.
• Cool air is returned by the CRAC units 721, 722, 723 to the cold portion 750 and is then drawn in to the cabinets 711, 712, 713, 714, 715, 716 to cool computing equipment housed therein, before being expelled to a corresponding hot aisle 761, 762, 763.
• Each hot aisle 761, 762, 763 comprises an aperture having a flow grid 731, 732, 733 arranged therein for allowing a bypass airflow to enter the hot aisle 761, 762, 763 from the cold area 750, including the cold aisles 751, 752, 753, 754.
• each flow grid was arranged to provide a single bypass airflow signal indicative of the bypass airflow through the flow grid. This is shown in a left-hand column of Figure 7(b), wherein, for example, the first warm air aisle 761 comprises the first flow grid 731 which provides a bypass airflow signal to control the first CRAC unit 721.
• each hot aisle 761, 762, 763 comprises a flow grid having a plurality of portions which each measure the bypass airflow there-through and provide a bypass airflow signal to control a corresponding one or more CRAC units.
• the first hot aisle 761 comprises the flow grid 731 divided into two portions which each independently provide a signal indicative of the velocity of the bypass airflow there-through.
• two separate flow girds may be arranged in the first hot aisle 761.
• a first portion Fl of the first flow grid 731 measuring bypass airflow into the first hot aisle 761 provides a bypass airflow signal to a control unit (not shown) which is arranged to control the first CRAC unit 721, whilst a second portion F2 of the flow grid 731 provides a bypass airflow signal to the control unit to control the second CRAC unit 722.
• the third flow grid 733 measuring bypass airflow into the third hot aisle 763 is divided into two portions F2, F3.
• the first portion F2 provides a bypass airflow signal to the control unit to control the second CRAC unit 722, whilst the second portion F3 provides a bypass airflow signal to the control unit to control the third CRAC unit 723.
• the second flow grid 732 measuring the bypass airflow to the second hot aisle 762 is divided into three portions Fl, F2, F3, each providing a signal indicative of the bypass airflow into the second hot aisle 762 to the control unit controlling the first, second and third CRAC units 721 , 722, 723, respectively.
• the control unit is arranged to increase a flow rate of cooled air into the cold portion 750 from the first and third CRAC units 721, 723 to maintain the predetermined velocity of bypass airflow into the second hot aisle 762.
• the control unit is arranged to control the second CRAC unit 722 to increase a flow rate of cooled air to maintain the predetermined velocity of bypass airflow to the first hot aisle 731.
• each flow grid 731 , 732, 733 comprises a portion providing a bypass airflow signal to control each of the CRAC units 721, 722, 723. That is, each flow grid 731, 732, 733 is divided into a number of portions Fl, F2, F3 equalling the number of CRAC units 721, 72, 722. Each portion Fl, F2, F3 of the flow grids is arranged to provide a bypass airflow signal to the control unit to control a corresponding CRAC unit 721, 722, 723.
• each flow grid 731, 732, 733 is divided into three portions Fl, F2, F3, each providing a bypass airflow signal to control a corresponding one of the CRAC units 721, 722, 723, although other numbers of portions and CRAC units may be envisaged.
• a corresponding drop in bypass airflow velocity into one or more hot aisles 761, 762, 763 is measured by the flow gird portions Fl, F2, F3 measuring bypass airflow into those hot aisles and the control unit is arranged to respond by increasing a flow rate of cooled air from the remaining CRAC units 721, 722, 723.
• failure or reduced operation of one or more CRAC units is compensated for by the remaining CRAC units.
• the flow grids may form a door or wall of a hot aisle 761, 762, 763.
• a flow grid 731 (a) may be divided into a single portion to provide a single bypass airflow signal.
• the flow grid 731 (b) may be horizontally divided into first and second portions Fl, F2 to each provide a bypass airflow signal.
• the flow grid 731(c) may be divided into first, second and third portions Fl, F2, F3, or into a different number of portions corresponding to the number of CRAC units. It will also be realised that other arrangements of flow grid division may be envisaged.
• FIGS 8(a) and (b) show a plan view and a cross section through a data centre 800 along a line A-A shown in Figure 8(a), a further embodiment of the present invention having N+l (3+1) redundancy and hot aisle containment, as in Figure 7, is shown.
• the data centre 800 comprises a cold portion 850 including cold aisles 851, 852 into which four CRAC units 821, 822, 823, 824 provide cooled air.
• Four hot aisles 861, 862, 863, 864 are formed between opposing pairs of computing cabinets 811-818.
• a flow grid 831, 832, 833, 834 is arranged to measure a bypass airflow into the respective hot aisle 861, 862, 863, 864.
• Warmed air is expelled from the cabinets 811-818 into a corresponding one of the hot aisles 861, 862, 863, 864 and the warm air is fed to the CRAC units 821, 822, 823, 834 through a hot air plenum or ducting 860.
• each flow grid 831, 833 is divided into four portions F1-F4, each corresponding to one of the CRAC units 821-824. Although only two flow grids 831, 833 are shown, the other flow grids 832, 834 have an equivalent division.
• each flow gird portion F1-F4 outputs a bypass airflow signal indicative of the bypass airflow through that portion to a control unit to control a corresponding one of the CRAC units 821-824.
• the control unit is arranged to control the remaining CRAC units to increase a flow rate of cooled air in order to maintain the predetermined level of bypass airflow into each hot aisle 861-864.
• FIG. 9(a) a layout of a data centre 900 having an exhaust air containment arrangement, similar to Figure 6, is shown.
• the data centre 900 comprises a plurality of cold aisles 951-955 interposing rows of cabinets 911, 912, 913, 914, 915, 916. Cooled air is supplied to the cold aisles by three CRAC units 921, 922, 923.
• Two different arrangements of flow grids are shown.
• a first arrangement comprises three flow grids 931, 932, 933 arranged in first, third and fifth cold aisles 951, 953, 955.
• a division of each flow grid is shown in Figure 9(b).
• the flow grids 931, 932, 933 are not divided and each output a bypass airflow signal to control a respective CRAC unit 931, 932, 933.
• a first arrangement of flow grids having N+l redundancy is shown in a middle column in which the first flow grid 931 is divided into two portions Fl, F2 providing bypass airflow signals to control the first and second CRAC units 931, 932 respectively.
• the second flow grid 932 is divided into three portions Fl, F2, F3 providing bypass airflow signals to control the first, second and third CRAC units 931, 932, 933, respectively.
• the third flow grid 933 is divided into two portions F2, F3 providing bypass airflow signals to control the second and third CRAC units 932, 933 respectively.
• flow grids 934, 935 are arranged in the second and third cold aisles 952, 954.
• the first flow grid 934 of the second arrangement is divided into two portions Fl, F2 to provide bypass airflow signals to control the first and second CRAC units 921, 922 respectively.
• the second flow grid 935 of the second arrangement is divided into two portions which provide bypass airflow signals to control the second and third CRAC units 922, 923 respectively.
• An arrangement of flow grids having N+2 redundancy is shown in the right hand column of Figure 9(b) and is the same as previously described with reference to Figure 7.
• FIG. 10 illustrates two further example arrangements of flow grids in a data centre 1000 having exhaust air containment.
• the data centre 1000 comprises four rows of cabinets 1011, 1012, 1013, 1014 which are supplied with cooled air by four CRAC units 1021, 1012, 1023, 1024.
• a flow grid 1031 which is divided into four portions Fl, F2, F3, F4 is centrally arranged in the data centre. Each portion of the flow grid 1031 provides a bypass airflow signal to control a respective one of the CRAC units 1021, 1012, 1023, 1024.
• the first portion Fl provides a bypass airflow signal to control the first CRAC unit 1021; the second portion F2 provides a bypass airflow signal to control the second CRAC unit 1022; the third portion F3 provides a bypass airflow signal to control the third CRAC unit 1023; and the fourth portion F4 provides a bypass airflow signal to control the fourth CRAC unit 1024.
• this arrangement minimises a complexity of the CRAC unit control system and requires only a single decoupling area in which the flow grid 1031 is located.
• four flow grids 1032, 1033, 1034, 1035 are arranged generally toward each corner of the data centre 1000.
• This arrangement requires more decoupling areas, but provides more responsive control of the CRAC units 1021, 1022, 1023, 1024 since the flow grids 1032, 1033, 1034, 1035 measure bypass airflow in different regions of the data centre 1000.
• a control unit controlling each of the CRAC units 1021, 1022, 1023, 1024 receives four bypass airflow signals indicative of the bypass airflow velocity. In the event that one of the four bypass airflow signals drops below the predetermined level, the appropriate control unit is arranged to increase the flow of cooled air from that CRAC unit to the data centre 1000.
• Figure 11 illustrates design considerations for embodiments of the present invention.
• Figure 11 schematically illustrates a data centre 1100 including a CRAC unit 1110, a flow grid 1130, a first server 1140 and a second server 1150.
• the first server 1140 represents a server that is located in the data centre 1100 near to the flow grid 1130 whilst the second server 1150 represents a server which is located in a region of the data centre distal from flow grid 1130.
• the flow grid experiences a constant pressure differential ⁇ P between the cold and hot portions of the data centre in which distal ends of the flow grid are located due to maintenance of the bypass airflow at the predetermined level.
• the first server 1140 also experiences the pressure differential ⁇ P between the cold and hot portions at both full and partial operating loads when differing flow rates of air are being drawn through the server 1140 for cooling. It is important to ensure that the differential pressure ⁇ P experienced by the first server 1140 is tolerable to a cooling control system of the server 1140.
• various pressure losses occur, such as in the air supply and return plenums, through air supply floor grilles, in the cabinet in which the sever is located etc.
• the pressure differential experienced by the second server 1150 is less than that of the first server 1140. If the pressure losses between the servers 1140, 1150 exceed the pressure differential ⁇ P at the first server 1140, then the second server 1150 may experience a negative pressure between the cold and hot portions of the data centre which would try to draw hot air from the hot portion through the server. Therefore, it should be ensured that the second server 1150 always experiences a positive pressure differential ⁇ P, even when the operation of one or both of the servers 1140, 1150 is at a minimum load.
• embodiments of the present invention provide accurate control of data centre cooling which optimally manages the output of CRAC units in response to a cooling throughput of computing equipment in a data centre. Furthermore, some embodiments of the present invention withstand situations in which one or more CRAC units have reduced operation, such as in a failure case.
• Embodiments of the present invention may be static data centres, such as data centres formed by a permanent structure e.g. a building.
• a moveable data centre may be a containerised data centre wherein computer equipment may be housed within a shipping container type structure.
• a moveable data centre may be a wheel-mounted container, such as a wagon or truck trailer.
• Other moveable data centres may be those mounted on or within a vessel, such as a ship.
• a moveable data centre may also be known as a portable on- demand data centre.

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• 2008
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